3.6 enthalpy

Question 1

what is hess’s law

Answer 1

Hess’s Law: the energy change of any chemical reaction is the same regardless of the route taken

Question 2

define an exothermic reaction

Answer 2

Exothermic reaction: gives out heat. More chemical energy present in the reactants than the products.

Question 3

define an endothermic reaction

Answer 3

Endothermic reaction: takes in heat. More chemical energy in the products than the reactants.

Question 4

define the Enthalpy change of reaction, Δf HΘ

Answer 4

the enthalpy change when the number of moles of the substances in the equation as written react under standard conditions of 298K and 101 kPa.

Question 5

define The standard enthalpy change of formation, ΔHfΘ

Answer 5

standard enthalpy of formation is the enthalpy change when 1 mole of a substance is formed from its elements, in their standard states, under standard conditions of 298K and 101 kPa.

Question 6

define the The standard enthalpy change of combustion

Answer 6

is the enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions of 298K and 101 kPa.

Question 7

define 1st ionisation energy

Answer 7

1st ionisation energy, ΔIEHΘ
:The energy required to remove one mole of electrons from one mole of atoms in the gaseous state.

Question 8

define electron affinity

Answer 8

1st electron affinity, Δ EA​ H Θ
: The enthalpy change that occurs when one mole of gaseous 1- ions are formed from gaseous atoms.

Question 9

define enthalpy change of solution

Answer 9

The standard enthalpy change of solution, ΔsolHΘ is the enthalpy change when one mole of a compound dissolves in water under standard conditions.

Question 10

define enthalpy change of hydration

Answer 10

The standard enthalpy of hydration, ΔhydHΘ is the enthalpy change that occurs when one mole of aqueous ions are formed from their gaseous ions under standard conditions.

Question 11

define standard enthalpy of atomisation

Answer 11

This is the enthalpy change that occurs when one mole of gaseous atoms is formed from the elements in its standard state.

Question 12

what is meant by lattice enthalphy

Answer 12

the energy released when one mole of ionic compound is formed from its constituent ions in the gaseous state, under standard conditions.

Question 13

define The standard enthalpy change of solution

Answer 13

is the enthalpy change when one mole of a compound dissolves in water under standard conditions.